pkg/time: fix hermeticity issue

Time parsing was dependent on Location.

Fixes #1522

Change-Id: Ibf43e2f89e92eb1660d8f24dd25ba5a7afc01c8b
Signed-off-by: Marcel van Lohuizen <mpvl@golang.org>

pkg/time/testdata/gen.txtar

@@ -6,6 +6,19 @@ import "time"
 t1: time.Time & "1937-01-01T12:00:27.87+00:20"
 t2: time.Time & "no time"
 t3: time.Unix(1500000000, 123456)
+
+parse: {
+	t1: time.Parse(time.RFC822, "01 Jul 21 17:54 CEST")
+	t1: time.Parse(time.RFC822, "01 Jul 21 17:54 CDST")
+	t1: time.Parse(time.RFC822, "01 Jul 21 17:54 PST")
+	t1: time.Parse(time.RFC822, "01 Jul 21 17:54 PDT")
+	t1: time.Parse(time.RFC822, "01 Jul 21 17:54 EST")
+	t1: time.Parse(time.RFC822, "01 Jul 21 17:54 EDT")
+
+	_layout: "01/02 03:04:05PM '06 -0700"
+	t2: time.Parse(_layout, _layout)
+}
+
 -- out/time --
 Errors:
 t2: invalid value "no time" (does not satisfy time.Time): error in call to time.Time: invalid time "no time":
@@ -15,4 +28,8 @@ Result:
 t1: "1937-01-01T12:00:27.87+00:20"
 t2: _|_ // t2: invalid value "no time" (does not satisfy time.Time): error in call to time.Time: invalid time "no time"
 t3: "2017-07-14T02:40:00.000123456Z"
+parse: {
+	t1: "2021-07-01T17:54:00Z"
+	t2: "2006-01-02T22:04:05Z"
+}
 

pkg/time/time.go

@@ -130,7 +130,7 @@ func Time(s string) (bool, error) {
 }
 
 func timeFormat(value, layout string) (bool, error) {
-	_, err := time.Parse(layout, value)
+	_, err := time.ParseInLocation(layout, value, nil)
 	if err != nil {
 		// Use our own error, the time package's error as the Go error is too
 		// confusing within this context.
@@ -175,17 +175,11 @@ func Format(value, layout string) (bool, error) {
 // location and zone in the returned time. Otherwise it records the time as
 // being in a fabricated location with time fixed at the given zone offset.
 //
-// When parsing a time with a zone abbreviation like MST, if the zone abbreviation
-// has a defined offset in the current location, then that offset is used.
-// The zone abbreviation "UTC" is recognized as UTC regardless of location.
-// If the zone abbreviation is unknown, Parse records the time as being
-// in a fabricated location with the given zone abbreviation and a zero offset.
-// This choice means that such a time can be parsed and reformatted with the
-// same layout losslessly, but the exact instant used in the representation will
-// differ by the actual zone offset. To avoid such problems, prefer time layouts
-// that use a numeric zone offset, or use ParseInLocation.
+// Parse currently does not support zone abbreviations like MST. All are
+// interpreted as UTC.
 func Parse(layout, value string) (string, error) {
-	t, err := time.Parse(layout, value)
+	// TODO: support named variadic argument "location:" to pass in a location.
+	t, err := time.ParseInLocation(layout, value, nil)
 	if err != nil {
 		return "", err
 	}